A sprayable hotmelt adhesive is already known. Thus, EP 0 442 045 B1 describes a sprayable hotmelt adhesive based on the above-mentioned poly-α-olefin with no more than 30% by weight of additives, more especially waxes and/or resins. Paraffinic or aromatic oils may also be used. The Examples contain ethene/propene/1-butene terpolymers and plastic microwaxes and, in some cases, even a hydrocarbon resin. The viscosities are in the range from 2,700 to 3,400 mPas at 190° C.
The Hüls technical information pamphlet entitled “Vestoplast: Klebrohstoff für Hot-Melt-Anwendungen (Vestoplast: an Adhesive Raw Material for Hotmelt Applications)” dating back to 1996 describes a number of atactic poly-α-olefin copolymers and terpolymers of the monomers ethylene; propylene and 1-butene. Polymers such these have excellent wetting behaviour on nonpolar substrates such as, for example, polyethylene and polypropylene. An increase in adhesive strength can be achieved by combination with tackifying resins or plasticizers. Recommended resins include, in particular, substantially saturated hydrocarbon resins. Added in a quantity of up to 30%, the resin acts as a plasticizer. Beyond 35%, the mixture assumes the properties of the resin and becomes hard and brittle. The tensile strength of a mixture of poly-α-olefin and resin in a ratio of 70:30 parts by weight falls by at least 20% when the ratio is changed to 50:50 parts by weight at the expense of the poly-α-olefin. Waxes are added inter alia for fine viscosity adjustment and to reduce stringing. In most cases, polybutenes of relatively low molecular weight are recommended as plasticizers. It costs less to use paraffinic or naphthenic mineral oils. The basic formulation for sprayable hotmelt adhesives for sanitary articles contains 70 parts of Vestoplast 704 (a poly-α-olefin), 25 parts of Escorez 5380 (a hydrogenated polycyclopentadiene), 5 parts of Napvis D 10 (a polybutene liquid at room temperature) and 0.4 part of Irganox 1010 (an antioxidant for polyolefins). This known sprayable hotmelt adhesive has a melt viscosity of 2,000 mPas at 190° C. and a softening point of 91° C. Unfortunately, it has poor adhesive properties. Thus, the initial adhesion values in particular are poor and deteriorate even further in the event of storage. Further disadvantages include a distinct reduction in the adhesion values in the wet state, the so-called “wet values” or “wet strength”. Since the adhesives described in the document in question are used in particular for the production of a composite material, for example for a composite material containing at least one nonwoven, it is essential that the adhesion values after storage and the wet adhesion values do not fall below the initial values. The adhesives are being used to an increasing extent in many areas of everyday life because, in general, they represent a simple, permanent and safe method of fixing materials. Composite materials of the type used in particular in the field of personal hygiene are generally materials with a limited useful life which are discarded, for example, after being used only once, more especially disposable products. Products such as these mainly include diapers, sanitary towels and panty liners etc. of which the function is to absorb bodily fluids such as, for example, urine and blood. In view of this fact, the adhesive used in the composite material must hold the material together even in the “wet” state. This is only possible if the so-called wet values are at the same level as the initial values.
EP 211 311 describes a self-adhesive absorbent shaped, body and a process for the production of a pressure-sensitive hotmelt adhesive suitable therefor. The pressure-sensitive hotmelt adhesive consists of 20 to 80% of substantially amorphous olefinic polymers, 20 to 80% of tackifying resins and 0 to 80% of plasticizer oil, the polymers being atactic and the pressure-sensitive hotmelt adhesive having a shear strength of less than 1 minutes (standard test against steel). Only one olefinic polymer is mentioned. It has a melt viscosity at 190° C. of ca. 50,000 mPas.
Accordingly, the problem addressed by the present invention was to improve adhesion, above all initial adhesion, but also adhesion after storage for a certain period and also wet adhesion. In addition, however, the adhesion levels would be made more independent of the processing conditions, more especially the spraying temperature, the quantity applied and the method of application. However, the spraying properties and other important processing and performance properties would not be adversely affected.